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            <h2 class="title" style="clear: both"><a id="cachesize"></a>Selecting the Cache Size</h2>
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      <p>
        Cache size is important to your application because if it is set to too
        small of a value, your application's performance will suffer from too
        much disk I/O. On the other hand, if your cache is too large, then your
        application will use more memory than it actually needs.
        Moreover, if your application uses too much memory, then on most
        operating systems this can result in your application being swapped out
        of memory, resulting in extremely poor performance.
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        You select your cache size using either
            
            
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                <code class="methodname">DatabaseConfig.setCacheSize()</code>, or 
                <code class="methodname">EnvironmentConfig.setCacheSize()</code>,
            </span>
         depending on whether you are using a database environment or not. You
         cache size must be a power of 2, but it is otherwise limited only by
         available memory and performance considerations.
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      <p>
        Selecting a cache size is something of an art, but fortunately you
        can change it any time, so it can be easily tuned to your
        application's changing data requirements.  The best way to
        determine how large your cache needs to be is to put your
        application into a production environment and watch to see how much
        disk I/O is occurring. If your application is going to disk quite a
        lot to retrieve database records, then you should increase the size
        of your cache (provided that you have enough memory to do so).
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      <p>
        You can use the <code class="literal">db_stat</code> command line utility with the
        <code class="literal">-m</code> option to gauge the effectiveness of your cache.
        In particular, the number of pages found in the cache is shown, along
        with a percentage value. The closer to 100% that you can get, the
        better. If this value drops too low, and you are experiencing
        performance problems, then you should consider increasing the size of
        your cache, assuming you have memory to support it.
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